<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>ID选择器</title>
    <style>
    #c1{
        height: 50px;
        color: blue;
    }
    </style>
</head>
<body>
<div id="c1">
      用户名：<input type="text" name="username">
</div>
</body>
</html>